SEOUL, South Korea (AP) — A team of U.S. investigators including representatives from Boeing have examined the site of a plane crash that killed 179 people in South Korea while authorities were conducting safety inspections on all Boeing 737-800 aircraft operated by the country’s airlines.

All but two of the 181 people aboard the Boeing 737-800 operated by South Korean budget airline Jeju Air died in Sunday’s crash. Video showed the aircraft, without its landing gear deployed, crash-landed on its belly and overshoot a runaway at South Korea’s southern Muan International Airport before it slammed into concrete fence and burst into a flame.

The plane was seen having an engine trouble, and preliminary examinations also say the pilots received a bird strike warning from the ground control center and issued a distress signal as well. But many experts say the landing gear issue was likely the main cause of the crash.

The South Korean government has launched safety inspections on all the 101 Boeing 737-800s in the country. The Transport Ministry said authorities are looking at maintenance and operation records during five days of safety checks that are to run until Friday.

The ministry said that a delegation of eight U.S. investigators — one from the Federal Aviation Administration, three from National Transportation Safety Board and four from Boeing — made an on-site visit to the crash site on Tuesday. The results of their examination weren’t immediately available.

Kim E-bae, Jeju Air’s president, told reporters Tuesday that his company will add more maintenance workers and reduce flight operations by 10-15% until March as part of efforts to enhance the safety of aircraft operations.

John Hansman, an aviation expert at MIT, said the crash was most likely the result of a problem with the plane’s hydraulic control systems. He said that would be consistent with the landing gear and wing flaps not being deployed “and might indicate a control issue which would explain the rush to get on the ground.”

The Boeing 737-800 ― an earlier version of 737 than the Max ― is a widely used plane with a good safety record, according to Najmedin Meshkati, an engineering professor at the University of Southern California who has studied aviation safety.

He said the failure of the plane’s system for broadcasting location, operating its landing gear and extending the wing flaps to slow down indicate a widespread problem that affected electrical and hydraulic systems. He is confident that investigators will learn what went wrong by analyzing information from the flight data and cockpit voice recorders.

“These are really the two pillars for accident analysis and accident reconstruction,” Meshkati said. Like other aviation experts, Meshkati also questioned the location of a solid wall just a few hundred feet (meters) past the end of the runway, given that planes occasionally do overshoot runways. “Having such a big concrete barrier over there was really very bad luck for this particular airplane,” he said.

South Korean officials have said they will look into whether the Muan airport’s localizer — a concrete fence housing a set of antennas designed to guide aircraft safely during landings — should have been made with lighter materials that would break more easily upon impact.

The crash was the deadliest disaster in South Korea’s aviation history in decades. A seven-day national mourning has been declared until Jan. 4.

The Transport Ministry said Tuesday that authorities have identified 175 bodies and are conducting DNA tests to identify the remaining five. Bereaved families said that officials told them that the bodies were so badly damaged that officials need time before returning them to relatives.

On Tuesday, Park Han Shin, a representative of the families, accused the government of failing to provide freezers on time as promised and said there are worries that the bodies could decompose. “The last dignities of the victims are seriously hurt. We strongly criticize authorities for failing to keep its promise,” Park said.

Associated Press writer David Koenig in Dallas contributed to this report.

SEOUL, South Korea (AP) — South Korean officials said Monday they will conduct safety inspections of all Boeing 737-800 aircraft operated by the country’s airlines, as they struggle to determine what caused a plane crash that killed 179 people a day earlier.

Sunday’s crash, the country’s worst aviation disaster in decades, triggered an outpouring of national sympathy. Many people worry how effectively the South Korean government will handle the disaster as it grapples with a leadership vacuum following the recent successive impeachments of President Yoon Suk Yeol and Prime Minister Han Duck-soo, the country’s top two officials, amid political tumult caused by Yoon’s brief imposition of martial law earlier this month.

New acting President Choi Sang-mok on Monday presided over a task force meeting on the crash and instructed authorities to conduct an emergency review of the country’s aircraft operation systems.

“The essence of a responsible response would be renovating the aviation safety systems on the whole to prevent recurrences of similar incidents and building a safer Republic of South Korea,” said Choi, who is also deputy prime minister and finance minister.

The Boeing 737-800 plane operated by South Korean budget airline Jeju Air aborted its first landing attempt for reasons that aren’t immediately clear. Then, during its second landing attempt, it received a bird strike warning from the ground control center before its pilot issued a distress signal. The plane landed without its front landing gear deployed, overshot the runway, slammed into a concrete fence and burst into a fireball.

Alan Price, a former chief pilot at Delta Air Lines and now a consultant, said the Boeing 737-800 is a “proven airplane” that belongs to a different class of aircraft than the Boeing 737 Max jetliner that was linked to fatal crashes in 2018 and 2019.

But South Korea’s Transport Ministry said Monday it plans to conduct safety inspections of all of the 101 Boeing 737-800 jetliners operated by the country’s airlines as well as a broader review into safety standards at Jeju Air, which operates 39 of those planes. Senior ministry official Joo Jong-wan said representatives from the U.S. National Transportation Safety Board and Boeing were expected to arrive in South Korea on Monday to participate in the investigation.

Ministry officials also said they will look into whether the Muan airport’s localizer — a concrete fence housing a set of antennas designed to guide aircraft safely during landings — should have been made with lighter materials that would break more easily upon impact.

Joo said the ministry has determined that similar concrete structures are in other domestic airports, including in Jeju Island and the southern cities of Yeosu and Pohang, as well as airports in the United States, Spain and South Africa.

Video of the crash indicated that the pilots did not deploy flaps or slats to slow the aircraft, suggesting a possible hydraulic failure, and did not manually lower the landing gear, suggesting they did not have time, said John Cox, a retired airline pilot and CEO of Safety Operating Systems in St. Petersburg, Florida.

Despite that, the jetliner was under control and traveling in a straight line, and damage and injuries likely would have been minimized if not for the barrier being so close to the runway, Cox said.

Other observers said the videos showed the plane was suffering from suspected engine trouble but the landing gear malfunction was likely a direct reason for the crash. They said there wouldn’t likely be a link between the landing gear problem and the suspected engine issue.

Earlier Monday, another Boeing 737-800 plane operated by Jeju Air returned to Seoul’s Gimpo International Airport shortly after takeoff when the pilot detected a landing gear issue. Song Kyung-hoon, a Jeju Air executive, said the issue was resolved through communication with a land-based equipment center, but the pilot decided to return to Gimpo as a precautionary measure.

Joo said officials were reviewing whether there might have been communication problems between air traffic controllers and the pilot. “Our current understanding is that, at some point during the go-around process, communication became somewhat ineffective or was interrupted, ahead of the landing and impact,” he said.

Ministry officials said Monday the plane’s flight data and cockpit audio recorders were moved to a research center at Gimpo airport ahead of their analysis. Ministry officials earlier said it would take months to complete the investigation of the crash.

The Muan crash is South Korea’s deadliest aviation disaster since 1997, when a Korean Airlines plane crashed in Guam, killing 228 people on board.

The crash left many South Koreans shocked and ashamed, with the government announcing a seven-day national mourning period through Jan. 4. Some questioned whether the crash involved safety or regulatory issues, such as a 2022 Halloween crush in Seoul that killed 160 people and a 2014 ferry sinking that killed 304 people.

The Transport Ministry said authorities have identified 146 bodies and are collecting DNA and fingerprint samples from the other 33.

Park Han Shin, a representative of the bereaved families, said they were told that the bodies were so badly damaged that officials need time before returning them to their families.

“I demand that the government mobilize more personnel to return our brothers and family members as intact as possible more swiftly,” he said, choking down tears.

The crash was yet more major news for South Koreans already reeling from a political crisis set off by Yoon’s martial law decree, which brought hundreds of troops into Seoul streets and revived traumatic memories of past military rule in the 1970-80s.

The political tumult resulted in the opposition-controlled National Assembly impeaching Yoon and Han. The safety minister stepped down and the police chief was arrested over their roles in the martial law inforcement.

The absence of top officials responsible for managing disasters has led to concerns.

“We are deeply worried whether the Central Disaster and Safety Countermeasures Headquarters really can handle the disaster,” the mass-circulation JoongAng Ilbo newspaper said in an editorial Monday.